CSharp lexical structure
Computer languages, like human languages, have a lexical structure. A source code of a C# program consists of tokens. Tokens are atomic code elements. In C#, we have comments, variables, literals, operators, delimiters and keywords.C# programs are composed of characters from the Unicode character set.
Comments
Comments are used by humans to clarify the source code. There are three types of comments in C#. Single-line comments, multi-line comments and XML comments. XML comments can be extracted to HTML files.Multi-line comments are enclosed by /* */ characters. Single line comments start with two forward slashes.
using System;Comments are ignored by the C# compiler.
/*
This is comments.cs
Author: Jan Bodnar
ZetCode 2010
*/
public class CSharpApp
{
// Program starts here
public static void Main()
{
Console.WriteLine("This is comments.cs");
}
}
/*Comments cannot be nested. The above code does not compile.
This is comments.cs
/* Author: Jan Bodnar */
ZetCode 2010
*/
White space
White space in C# is used to separate tokens in the source file. It is also used to improve readability of the source code.int i = 0;White spaces are required in some places. For example between the
int keyword and the variable name. In other places, it is forbidden. It cannot be present in variable identifiers or language keywords. int a=1;The amount of space put between tokens is irrelevant for the C# compiler.
int b = 2;
int c = 3;
Variables
A variable is an identifier, which holds a value. In programming we say, that we assign a value to a variable. Technically speaking, a variable is a reference to a computer memory, where the value is stored. Variable names can have alphanumerical characters and underscores. An identifier may begin with a character or an underscore. It may not begin with a number. Variable names are case sensitive. This means, that Name, name or NAME refer to three different variables. Variable names also cannot match language keywords. (In fact, we can use keywords as identifiers, if we precede them with @ character. But it is not a good programming practice.)string name23;These are valid C# identifiers.
int _col;
Date birth_date;
string 23name;These are invalid C# identifiers.
int %col;
Date birth date;
using System;Identifiers are case sensitive. Name and name are two different identifiers. In Visual Basic, a close cousin of the C# language, this would not be possible. In this language, variable names are not case sensitive.
public class CSharpApp
{
static void Main()
{
string name = "Robert";
string Name = "Julia";
Console.WriteLine(name);
Console.WriteLine(Name);
}
}
$ gmcs identifiers.cs
$ ./identifiers.exe
Robert
Julia
Literals
A literal is a textual representation of a particular value of a type. Literal types include boolean, integer, floating point, string, character, and date. Technically, a literal will be assigned a value at compile time, while a variable will be assigned at runtime.int age = 29;Here we assign two literals to variables. Number 29 and string "Hungarian" are literals.
string nationality = "Hungarian";
using System;In the above example, we have other literals. The bool literal may have value
public class CSharpApp
{
static void Main()
{
bool sng = true;
string name = "James";
string job = null;
double weight = 68.5;
DateTime born = DateTime.Parse("November 12, 1987");
Console.WriteLine("His name is {0}", name);
if (sng)
{
Console.WriteLine("He is single");
} else
{
Console.WriteLine("He is in a relationship");
}
Console.WriteLine("His job is {0}", job);
Console.WriteLine("He weighs {0} kilograms", weight);
Console.WriteLine("He was born in {0}",
string.Format("{0:yyyy}", born));
}
}
true or false. James is a string literal. The null represents the default value of any data type. 23 is an Integer literal. 68.5 is a floating point literal. Finally, the November 12, 1987 is a date literal. $ ./literals.exeThis is the output of the program.
His name is James
He is single
His job is
He weighs 68.5 kilograms
He was born in 1987
Operators
An operator is a symbol used to perform an action on some value. Operators are used in expressions to describe operations involving one or more operands.+ - * / % ^ & | ! ~This is a partial list of C# operators. We will talk about operators later in the tutorial.
= += -= *= /= %= ^= ++ --
== != < > &= >>= <<= >= <=
|| && >> << ?:
Separators
A separator is a sequence of one or more characters used to specify the boundary between separate, independent regions in plain text or other data stream.[ ] ( ) { } , : ;
string language = "C#";The double characters are used to mark the beginning and the end of a string. The semicolon (;) character is used to end each C# statement.
Console.WriteLine("Today is {0}", DateTime.Today.ToString("M/d"));
Parentheses (round brackets) are used to mark the method signature. The signature consists of method parameters. Curly brackets are used to denote the evaluated value. int[] array = new int[5] {1, 2, 3, 4, 5};
The square brackets [] are used to denote an array type. They are also used to access or modify array elements. The curly brackets {} are also used to initiate arrays. The curly brackets are also used in variable interpolation or to enclose the body of a method or a class. int a, b, c;The comma character can be used to use multiple declarations on the same line of code.
Keywords
A keyword is a reserved word in the C# language. Keywords are used to perform a specific task in the computer program. For example, define variables, do repetitive tasks or perform logical operations.C# is rich in keywords. Many of them will be explained in this tutorial. The keywords include if, else, for, while, base, false, float, catch, this and many others.
using System;In the above example, we use several keywords. using, public, static, void, int, for are C# keywords.
public class CSharpApp
{
static void Main()
{
int i;
for(i = 0; i<= 5; i++)
{
Console.WriteLine(i);
}
}
}
In this part of the C# tutorial, we covered the basic lexis for the C# language.
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